1. Field of the Invention
The invention relates generally to apparatus for the oxidation or the stabilization of continuous lengths of organic filamentary material. More specifically, the invention relates to an improved pyrolysis furnace for use in oxidation or stabilization apparatus wherein a continuous length of precursor filamentary material moves through the pyrolysis furnace and a part of gaseous by-products of the pyrolysis process are drawn out from the furnace through a conduit connecting to the body of the furnace and having a shutting means for shutting the movement of gas in the conduit and an injecting means for injecting water in the form of liquid or in the form of steam into the conduit which are operable to put out a fire of burning tar adhering to the inner wall of the conduit. The fire is caused by abnormal burning of filaments in the furnace.
2. Description of the Prior Art
In the past, it has been known to oxidize or stabilize continuous length of organic filamentary material for producing oxidized or stabilized filaments. The oxidized or stabilized filaments are used as fibers which are fire-proof fibers to an ordinary match flame. They are also used as reinforcing fibers in slate or concrete board instead of asbestos fibers or as precursor filaments for producing carbon filaments or graphite filaments.
Carbon filaments may be produced by subjecting organic filamentary material such as polyacrylonitrile filaments to specific conditions of temperature and surrounding atmosphere. Thus, in a first stage, the filaments may be heated to a temperature in the range from 200.degree. C. to 300.degree. C. in an oxidizing atmosphere such as air or air enriched with oxygen where upon they are converted into oxidized filaments. In a second stage the oxidized filaments may be heated at a temperature in excess of 1000.degree. C. in an inert atmosphere such as nitrogen. If graphitized filaments are to be produced further heat-treating is necessary which takes place at a temperature which is higher than 2000.degree. C. in an inert atmosphere such as nitrogen.
Recently, production of composite material comprising carbon fibers and resin or carbon fibers and metal became active, and development of mass production process and apparatus for producing oxidized fibers and carbon fibers are demanded.
It is known that in the oxidizing process an oxidizing reaction is carried out and the reaction involves calorification. It is also known that if an abnormal storage of heat occurs on the filaments staying in the furnace, a runaway reaction takes place. It is important to prevent the runaway reaction in the production of the oxidized fibers. Various prior process conditions have been proposed for preventing the runaway reaction, some of which have been practiced in commercial processes.
To satisfy the demand for a mass production process and apparatus, an oxidizing apparatus having a very large output was developed. In the apparatus, the running speed of the filaments passing through the furnace is very high and a large number of filaments are introduced continuously into the furnace at once. The apparatus is designed to prevent the runaway reaction to the extent possible. The process conditions in the oxidizing process in the apparatus are also selected to prevent the runaway reaction to the extent possible. An abnormal running of filaments and a breakage of filaments in the apparatus are sometimes observed. The abnormal running of the filaments or the breakage of the filaments is one of the causes of the runaway reaction. If the apparatus has filaments guiding rollers within the treating chamber, a coiling of the filament around the roller, caused by the breakage of the filament is too apt to occur causing the runaway reaction. In the large scale oxidizing furnace there are a great many causes of the runaway reaction compared to the conventional small scale oxidizing furnace, because the speed of the running filaments in the large scale oxidizing furnace is very high and the number of filaments also very large. On the other hand, a large amount of gaseous by-products come from the oxidizing compared to the conventional small scale furnace and are drawn out from the body of the furnace through a conduit connected to the body. The by-products are mainly decomposition products of the filaments such as HCN, CO and decomposition products of an oiling agent on the filaments. The by-products include tar-like substance. This tar-like substance exists in the vapor state at temperatures of more than about 200.degree. C. At temperature lower than about 200.degree. C., the vapor condenses quickly and becomes the so called tar. If the conduit for extracting the gaseous by-products is not separately heated, then much of the tar adheres to the inner wall of the conduit. The quantity of adhered tar observed in the large scale oxidizing furnace is very large compared to the conventional small scale oxidizing furnace. Thus, once the runaway reaction happens in the body of the large scale oxidizing furnace, the tar adhering to the conduit catches fire. The fire rapidly spreads along the length of the conduit. The fire damages the apparatus and causes pollution problems. Reducing the damage and solving the problem of pollution is a serious problem for a person who has control over the large scale oxidizing furnace.